1. Field of the Invention
The present invention relates to a wireless power supply technique.
2. Description of the Related Art
In recent years, in order to supply electric power to an electronic device, contactless power transmission (which is also referred to as “contactless power supply” or “wireless power supply”) has begun to come into commonplace use. In order to advance the compatibility of products between manufacturers, the WPC (Wireless Power Consortium) has been organized, and the WPC has developed the Qi standard as an international standard.
A wireless power supply that conforms to the Qi standard makes use of electromagnetic induction between a transmission coil and a reception coil. The power supply system comprises a power supply apparatus including a transmission coil and a power receiving terminal including a reception coil. In the power supply operation, the power supply apparatus and the power receiving terminal are neither mechanically bound nor coupled with each other. Thus, the relative positions of the transmission coil and the reception coil can be set as desired. Furthermore, it is conceivable that a foreign substance such as a piece of metal can be interposed between the transmission coil and the reception coil. The degree of coupling between the transmission coil and the reception coil can change due to such causes
With wireless power supply that conforms the Qi standard, by controlling the transmission power by means of communication between the power receiving terminal and the power supply apparatus, such an arrangement allows required electric power to be supplied to the power receiving terminal even if the transmission coil and the reception coil couple with a poor degree of coupling. In other words, even if power cannot be supplied with high efficiency, power supply is maintained by best-effort coupling. Thus, there is room for further improvement from the viewpoint of power efficiency.